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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Synthetic shibkovite K(K{sub 1.67}H{sub 2}O{sub 0.33})(Ca{sub 1.3}Na{sub 0.7})[Zn{sub 3}Si{sub 12}O{sub 30}]: the crystal structure and comparative crystal chemistry

The structure of a single crystal of a synthetic analog of mineral shibkovite K(K{sub 1.67}H{sub 2}O{sub 0.33})(Ca{sub 1.3}Na{sub 0.7})[Zn{sub 3}Si{sub 12}O{sub 30}] (milarite structure type) obtained by hydrothermal synthesis in the AlPO{sub 4}-K{sub 3}PO{sub 4}-CaCO{sub 3}-Na{sub 2}CO{sub 3}-ZnCO{sub 3}-SiO{sub 2}-H{sub 2}O system has been solved (R = 0.0406) by X-ray diffraction analysis: a = 10.5327(2) Å, c = 14.2019(3) Å, sp. gr. P6/mcc, Z = 2, and ρ{sub calcd} = 2.90 g/cm{sup 3}. The crystal-chemical features of the new phase are studied in comparison with the other terms of the milarite group. It is shown that the crystallization conditions for minerals and synthetic analogs of this group determine the presence or absence of crystallization water in the structures of compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Mn{sub 0.1}Ag{sub 0.9}In{sub 4.7}S{sub 7.6} single crystals: Crystal structure, band gap, and thermal expansion

Mn{sub 0.1}Ag{sub 0.9}In{sub 4.7}S{sub 7.6} single crystals are for the first time grown by the Bridgman method (vertical variant). The single crystals crystallize in the cubic spinel structure. The band gap of the single crystals is determined from the transmittance spectra in the region of the fundamental absorption edge at temperatures of T = 295 and 80 K. Thermal expansion is studied by the dilatometric method in the temperature range 80–500 K. The coefficients of thermal expansion, the Debye temperatures, and the rms (root mean square) dynamic displacements of atoms are calculated.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Crystallization and preliminary X-ray diffraction study of phosphopantetheine adenylyltransferase from M. tuberculosis crystallizing in space group P3{sub 2}

Crystals of M. tuberculosis phosphopantetheine adenylyltransferase were grown in microgravity by the capillary counter-diffusion method through a gel layer. The X-ray diffraction data set suitable for the determination of the three-dimensional structure at atomic resolution was collected from one crystal at the Spring-8 synchrotron facility to 2.00-Å resolution. The crystals belong to sp. gr. P3{sub 2} and have the following unit-cell parameters: a = b = 106.47 Å, c = 71.32 Å, α = γ = 90°, β = 120°. The structure was solved by the molecular-replacement method. There are six subunits of the enzyme comprising a hexamer per asymmetric unit. The hexamer is a biologically active form of phosphopantetheine adenylyltransferase from M. tuberculosis.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Individual phase constitutive properties of a TRIP-assisted QP980 steel from a combined synchrotron X-ray diffraction and crystal plasticity approach

Microstructure-based constitutive models for multiphase steels require accurate constitutive properties of the individual phases for component forming and performance simulations. We address this requirement with a combined experimental/theoretical methodology which determines the critical resolved shear stresses and hardening parameters of the constituent phases in QP980, a TRIP assisted steel subject to a two-step quenching and partitioning heat treatment. High energy X-Ray diffraction (HEXRD) from a synchrotron source provided the average lattice strains of the ferrite, martensite, and austenite phases from the measured volume during in situ tensile deformation. The HEXRD data was then input to a computationally efficient, elastic-plastic self-consistent (EPSC) crystal plasticity model which estimated the constitutive parameters of different slip systems for the three phases via a trial-and-error approach. The EPSC-estimated parameters are then input to a finite element crystal plasticity (CPFE) model representing the QP980 tensile sample. The predicted lattice strains and global stress versus strain curves are found to be 8% lower that the EPSC model predicted values and from the HEXRD measurements, respectively. This discrepancy, which is attributed to the stiff secant assumption in the EPSC formulation, is resolved with a second step in which CPFE is used to iteratively refine the EPSC-estimated parameters. Remarkably close agreement is obtained between the theoretically-predicted and experimentally derived flow curve for the QP980 material.

Hu, X. H. (ORCID:0000000277355091)↗
DOE OSTI2019

Hydrothermal Crystal Growth of Rare Earth Tin Cubic Pyrochlores, RE 2 Sn 2 O 7 (RE = La–Lu): Site Ordered, Low Defect Single Crystals

A hydrothermal route to single crystals of rare earth stannates RE 2 Sn 2 O 7 (RE = La–Lu) in the cubic pyrochlore structure is reported. Growth reactions were performed in aqueous fluids at 700 °C and 200 MPa with CsF mineralizers in concentrations ranging from 0 to 30 M, with 20 M CsF providing the most consistent results. Single crystals of the entire range of lanthanides were grown and characterized by single crystal X-ray diffraction and found to be isostructural in the Fd $\bar{3}$ m space group. The unit cell sizes range from 10.7106(16) Å for La 2 Sn 2 O 7 to 10.3005(9) Å for Lu 2 Sn 2 O 7 . Both the unit cell size and RE–O distances are found to be essentially linear with respect to the ionic radius of the rare earth ion. The high quality diffraction data strongly indicates that there is very little site disorder or lattice defects in the sample. Of specific interest is the synthesis and single crystal growth of Ce 2 Sn 2 O 7 , which represents one of the few f 1 pyrochlore samples. Specific heat measurements were obtained down to 50 mK on both Yb 2 Sn 2 O 7 and Ce 2 Sn 2 O 7 , with the Yb material displaying a single sharp peak at 138 mK suggesting that the sample does not contain any site disorder or “lattice stuffing”. The Ce analog demonstrates only a broad featureless transition below 100 mK, with this lack of long-range magnetic order consistent with quantum spin liquid behavior

36 MATERIALS SCIENCE↗
DOE OSTI2021

On the Origin of Room-Temperature Amplified Spontaneous Emission in CsPbBr 3 Single Crystals

CsPbBr 3 is an all-inorganic halide perovskite with excellent photoluminescence (PL) properties for laser applications. Amplified spontaneous emission (ASE) is a prerequisite for lasing and typically observed from low-dimensional CsPbBr3 nanostructures, where quantum confinement enhances ASE. However, a gain medium for lasing should be prepared into a robust bulk form that works under intense light illumination. Here, we demonstrate that bulk CsPbBr 3 single crystals exhibit highly efficient ASE with a threshold of 46 MWcm -2 at 520 nm, if PL reabsorption via the indirect Rashba gap is properly suppressed by thickness control. Based on a series of spectroscopic and microscopic measurements, we show that this below-the-gap absorption can significantly alter the PL feature and even the apparent color of the crystal depending on the crystal size. Our results show that a thin CsPbBr 3 single crystal can be utilized for lasing applications when engineered into a submillimeter thickness for effective light–matter interaction.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Crystal Growth, Single Crystal Structure, and Biological Activity of Thiazolo-Pyridine Dicarboxylic Acid Derivatives

Four novel TPDCA derivatives were prepared via a supersaturation method combining TPDCA with water, N-methyl-2-pyrrolidone (NMP), Na(PO 2 H 2 ), and ammonia solution: 2(C 9 H 7 NO 5 S)H 2 O (1), (C 9 H 7 NO 5 S)C 5 H 9 NO (2), (C 9 H 7 NO 5 S)Na(PO 2 H 2 ) (3), and (C 9 H 5 NO 5 S)(NH 4 )2(H 2 O) (4). Their crystal structures were determined by single-crystal X-ray diffraction. Compounds (1) and (2) crystallize in the monoclinic space groups P2 1 and P2 1 /c, respectively, whereas compounds (3) and (4) crystallize in the triclinic space group P1 - . Weak and moderate hydrogen bonds were detected in the four compounds. In the biological tests, (1) and (3) exhibited significant antibacterial activity against Escherichia coli and Staphylococcus aureus; in addition, (1) was cytotoxic against leukemia HL-60 cells with the IC 50 value of 158.5 ± 12.5 μM.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Enhancement of crystal homogeneity of protein crystals under application of an external alternating current electric field

X-ray diffraction rocking-curve measurements were performed on tetragonal hen egg white (HEW) lysozyme crystals grown with and without the application of an external alternating current (AC) electric field. The crystal quality was assessed by the full width at half maximum (FWHM) value for each rocking curve. For two-dimensional maps of the FWHMs measured on the 440 and the 12 12 0 reflection, the crystal homogeneity was improved under application of an external electric field at 1 MHz, compared with that without. In particular, the significant improvement of the crystal homogeneity was observed for the 12 12 0 reflection.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Ultra-fast solid state electro-optical modulator based on liquid crystal polymer and liquid crystal composites

A different generation of polymer-dispersed liquid crystals (PDLCs) based on a liquid crystalline polymer host is reported wherein the fluid behavior of the reactive mesogenic monomer is an enabler to concentration windows (liquid crystal polymer/liquid crystal) (and subsequent morphologies) not previously explored. These liquid crystal (LC) polymer/LC composites, LCPDLCs, exhibit excellent optical and electro-optical properties with negligible scattering losses in both the ON and OFF states. These systems thus have application in systems where fast phase modulation of optical signal instead of amplitude control is needed. Polarized optical microscopy and high resolution scanning electron microscopy confirm a bicontinuous morphology composed of aligned LC polymer coexisting with a phase separated LC fluid. Operating voltages, switching times, and spectra of LCPDLCs compare favourably to conventional PDLC films. The LCPDLCs exhibit a low switching voltage (4–5 V/μm), symmetric and submillisecond (200 μs) on/off response times, and high transmission in both the as formed and switched state in a phase modulation geometry.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Computationally efficient dielectric calculations of molecular crystals

The microscopic dielectric response is a key quantity for electronic materials such as organic semiconductors. Calculations of this response for molecular crystals are currently either expensive or rely on extreme simplifications such as multipole expansions which lack microscopic detail. We present an alternate approach using a microscopic analogue of the Clausius-Mossotti equation, which constructs the dielectric response of a crystal from an eigenvalue decomposition of the dielectric response of individual molecules. This method can potentially be used to examine the effects of defects, disorder, and surfaces on the dielectric properties of molecular solids.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Lineshape spectroscopy with a very high resolution, very high signal-to-noise crystal spectrometer

We have developed a high-resolution x-ray spectrometer for measuring the shapes of spectral lines produced from laser-irradiated targets on the Orion laser facility. The instrument utilizes a spherically bent crystal geometry to spatially focus and spectrally analyze photons from foil or microdot targets. The high photon collection efficiency resulting from its imaging properties allows the instrument to be mounted outside the Orion chamber, where it is far less sensitive to particles, hard x-rays, or electromagnetic pulses than instruments housed close to the target chamber center in ten-inch manipulators. Moreover, Bragg angles above 50° are possible, which provide greatly improved spectral resolution compared to radially viewing, near grazing-incidence crystal spectrometers. These properties make the new instrument an ideal lineshape diagnostic for determining plasma temperature and density. We describe its calibration on the Livermore electron beam ion trap facility and present spectral data of the K-shell emission from highly charged sulfur produced by long-pulse as well as short-pulse beams on the Orion laser in the United Kingdom.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Design of a cryo-cooled artificial channel-cut crystal monochromator for the European XFEL

An artificial channel-cut crystal monochromator for the hard X-Ray beamlines of SASE 1&2, cryogenically cooled by the so-called pulse tube cooler (cryorefrigerator), is currently under development at the European XFEL ( http://www.xfel.eu/ ). The fabrication is on-going. We present here the crystal optical consideration and the novel cooling configuration, according to the X-Ray FEL pulses proprieties. The mechanical design improvements are pointed out as well to implement such kind of monochromator based on the previous similar design.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Design of nematic liquid crystals to control microscale dynamics

The dynamics of small particles, both living such as swimming bacteria and inanimate, such as colloidal spheres, has fascinated scientists for centuries. If one could learn how to control and streamline their chaotic motion, that would open technological opportunities in the transformation of stored or environmental energy into systematic motion, with applications in micro-robotics, transport of matter, guided morphogenesis. This review presents an approach to command microscale dynamics by replacing an isotropic medium with a liquid crystal. Orientational order and associated properties, such as elasticity, surface anchoring, and bulk anisotropy, enable new dynamic effects, ranging from the appearance and propagation of particle-like solitary waves to self-locomotion of an active droplet. By using photoalignment, the liquid crystal can be patterned into predesigned structures. In the presence of the electric field, these patterns enable the transport of solid and fluid particles through nonlinear electrokinetics rooted in anisotropy of conductivity and permittivity. Director patterns command the dynamics of swimming bacteria, guiding their trajectories, polarity of swimming, and distribution in space. This guidance is of a higher level of complexity than a simple following of the director by rod-like microorganisms. Namely, the director gradients mediate hydrodynamic interactions of bacteria to produce an active force and collective polar modes of swimming. The patterned director could also be engraved in a liquid crystal elastomer. When an elastomer coating is activated by heat or light, these patterns produce a deterministic surface topography. The director gradients define an activation force that shapes the elastomer in a manner similar to the active stresses triggering flows in active nematics. Finally, the patterned elastomer substrates could be used to define the orientation of cells in living tissues. The liquid-crystal guidance holds a major promise in achieving the goal of commanding microscale active flows.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Optical emission diagnostics of plasmas in chemical vapor deposition of single-crystal diamond

A key aspect of single crystal diamond growth via microwave plasma chemical vapor deposition is in-process control of the local plasma–substrate environment, that is, plasma gas phase concentrations of activated species at the plasma boundary layer near the substrate surface. Emission spectra of the plasma relative to the diamond substrate inside the microwave plasma reactor chamber have been analyzed via optical emission spectroscopy. The spectra of radical species such as CH, C{sub 2}, and H (Balmer series) important for diamond growth were identified and analyzed. The emission intensities of these electronically excited species were found to be more dependent on operating pressure than on microwave power. Plasma gas temperatures were calculated from measurements of the C{sub 2} Swan band (d{sup 3}Π → a{sup 3}Π transition) system. The plasma gas temperature ranges from 2800 to 3400 K depending on the spatial location of the plasma ball, microwave power and operating pressure. Addition of Ar into CH{sub 4}+H{sub 2} plasma input gas mixture has little influence on the Hα, Hβ, and Hγ intensities and single-crystal diamond growth rates.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Evaluation of sucrose crystallization kinetics using confocal microscopy: Determining differences in sucrose crystallization kinetics between single and polycrystal studies

Sucrose solution crystal growth kinetics are dependent on temperature, concentration, and impurities. A double polarized confocal microscopy system was used to obtain photographs with high contrast between growing crystals and the background for color background removal image processing. Seeded solutions of 72 wt% sucrose at 27, 35, 45, and 55°C were compared for single and polycrystals. Polycrystal analysis was determined to offer more rapid image processing and to be more applicable to systems in real operating conditions, while single-crystal analysis was determined to give more comprehensive descriptions of individual crystal behavior at the cost of slower processing.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Single-Crystal-to-Single-Crystal Post-Synthetic Modifications

Chalcogenides are the cornerstone of the semiconductor and thermoelectric industries and are up-and-coming materials for superconductors, catalysis, and battery applications. Challenges in synthesizing those materials emerge from the chalcogen's volatility and the tendencies of chalcogenides to react with even trace quantities of oxygen. Many techniques have been applied to the growth of chalcogenide single crystals, which are convenient for structure determinations and intrinsic property measurements. One of the recent advances in chalcogenide chemistry is the intriguing single-crystal-to-single-crystal (SCSC) transformation, leading to new metastable compositions. Post-synthetic transformations are well-known and studied for chalcogenide powders; however, examples of post-synthetic conversions that retain single crystallinity are rare. To date, the scope of SCSC reactions includes (de)intercalation in the layered compositions and ion exchange in open-framework materials, salt-inclusion chalcogenides, and layered structures. This poster will discuss the successful examples of SCSC modifications monitored by single-crystal X-ray diffraction (SC-XRD), emphasizing how post-synthetic transformations affect materials' properties.

chalcogenide↗